This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The purpose of this research is to perform a study that shows it is possible to simulate a lunar/moon mission by using a lunar/moon bed rest analog. This study is trying to establish a real-life situation for understanding the effects of lunar gravity on physiological changes while astronauts are on the moon. Participation in this study may last 6-8 weeks and involves three phases - a before-bed rest phase, a bed rest phase (includes 6 days of bed rest at 9.5-degree of head-up tilt), and an after-bed rest phase (includes reconditioning).During the pre- UTMB time (BR-30 to BR-4) the Bruce Treadmill Test will assess the pre-bed rest level of aerobic fitness of subjects. The Daily Activity Log which records activities and duration will be completed for 7 days during this period. The MRI test will be used to determine leg muscle volumes once at the start of pre Bed-Rest after admission to UTMB and once at the end of Bed Rest. The Plasma Volume test will be performed once at the start of pre Bed-Rest after admission to UTMB and once at the end of Bed Rest. The Comfort Assessment Log will record comfort level of test subjects three times a day during the Bed Rest Phase. NASA scientists hope to get information that will determine if this study can establish a real-life situation for understanding the effects of lunar gravity on physiological changes while astronauts are on the moon.